A cover mounting device of the aforementioned type is described in German patent document (open application) DE-OS No. 30 37 455. In this device the roller interacting with the grooved cam plate, i.e. the cam-follower roller is mounted on the free end of the roller lever, on a joint of which is mounted an intermediate lever connected by its free end to the supporting shaft via the rod system.
In practice it has been found that if the cover mounting device is blocked, e.g. because a cover is jammed in the cover magazine, a jerk occurs in the driving mechanism, the follower roller being thus lifted out of the grooved cam trajectory while the device is blocked. As a consequence the cam trajectory must be left open at one end. Apart from an unnecessary construction expense, the open end of the cam groove can prevent the device from running.